1. Technical Field
The subject matter described herein relates to the design of devices for controlling the flow of light and radiant heat through selective reflection, transmission, and/or absorption and re-emission. The technology has particular, but not exclusive, application in passive or active light-regulating and temperature-regulating films, materials, and devices, especially as construction or building materials.
2. Description of the Related Art
Numerous electrochromic building materials have been developed, such as the electrochromic windows manufactured by Sage Electrochromics and Research Frontiers. In addition, numerous thermochromic building materials have been developed, including the thermoabsorptive and thermoreflective window filters manufactured by RavenBrick LLC. Such systems are often described as “dynamic glazings” or “dynamic windows.” Thermochromic and electrochromic materials may also be incorporated into opaque wall panels.
All thermochromic and electrochromic building materials share a number of common traits. First, they all transmit a variable amount of energy in the form of ultraviolet, visible, and near infrared light. Second, they all possess minimum and maximum transmission values in their clear and tinted states. The difference between these two values is sometimes referred to as the “throw.” Third, they all possess a minimum and a maximum wavelength over which their variable properties operate. The difference between these two values is called the “bandwidth” of the device, and the values themselves are known as the “band edges.” Finally, they all possess one or more wavelength ranges over which they do not operate. Typically the ultraviolet wavelengths are simply blocked to prevent them from damaging the dynamic building material and/or to prevent them from passing through into the building interior. In addition, while it may seem desirable to extend the band edge of a dynamic building material to cover the entire solar spectrum, in practice it becomes increasingly difficult to extend the band edge deep into the infrared, and the benefits of doing so are increasingly sparse as the energy of sunlight peaks at around 460 nanometers and tails off thereafter according to Boltzmann's law.
Thus, a band edge of 1000 nanometers encompasses roughly 73% of the sun's energy and a band edge of 1200 nanometers encompasses roughly 81% of the sun's energy, while a band edge encompassing 99% of the sun's energy does not occur until a wavelength of 4000 nanometers. In practice, this diminishing return means that dynamic building materials rarely exhibit band edges significantly beyond 1200 nm. For purposes of this document, the infrared output of the sun that falls outside the band edge of a dynamic building material shall be referred to as the “unswitched infrared band,” and represents a substantial energy resource that is typically wasted.
The information included in this Background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded as subject matter by which the scope of the invention is to be bound or limited.